The statistics snafu comes as the department is facing increased scrutiny over how budget reductions have affected service.

The dust-up began Thursday, when candidate Austin Beutner complained in a Huffington Post column that recent Fire Department budget cuts have sent response times for medical emergencies soaring. Beutner laid the blame on the City Council members who approved the cuts, singling out mayoral rivals Eric Garcetti and Jan Perry. He also criticized another opponent, City Controller Wendy Greuel, for failing to scrutinize the effect of the cuts.

Relying on Fire Department reports presented to lawmakers, Beutner said that in 2008 the department responded to medical emergencies within five minutes 86% of the time. After the cuts, the department last year met that standard just 59% of the time, he said.

Following Beutner's critique — and a Times inquiry — the department made an awkward admission: Data showing it did so well in the past were simply wrong.

Federal guidelines call for first responders to arrive on scene in under five minutes 90% of the time. But a former department statistician counted all responses within six minutes, officials explained, which improved the record. Retired Capt. Billy Wells, who crunched the data with a hand calculator, said he followed the department's long tradition of using a six-minute response standard.

Wells' successor, Capt. Mark Woolf, said he reluctantly continued using the flawed formula for a time because he didn't want to be blamed for a sudden drop in department performance. "I didn't want to touch that [extra] minute because I knew the data would take a dump," he said.

Corrected data generated by a new computer system shows that in 2008, the department actually hit the five-minute goal only 64% of the time, officials said. By last year, that number had fallen to about 60%.

Fire Chief Brian Cummings said his department's performance is pretty good, given the 16% reduction to its budget in recent years, which has led to the elimination of firetrucks or ambulances at about one-fourth of the city's 106 fire stations.